Kaposi's sarcoma (KS), caused by the Kaposi's sarcoma-associated herpes virus (KSHV), is a major cancer associated with AIDS and a global health challenge. The tumor is characterized by intense angiogenesis and the proliferation of spindle cells that can affect the skin, mucosa and viscera, causing significant morbidity. Understanding the role of viral and cellular genes leading to KS carcinogenesis is paramount to developing rationally designed therapies for KS. A collaboration between the Mesri and Goldschmidt labs has led to the identification of the Rac1 GTPase, a signaling mediator that triggers production of reactive oxygen species (ROS) by non-phagocytic NADPH-oxidase (NOX), as a potential major player in KS. We have found that expression of a constitutively-active Rac1 mutant (RacCA) driven by -smooth muscle actin (-SMA) promoter in transgenic mice led to the formation of lesions that strongly resemble those of Kaposi's sarcoma. Significantly, RacCA--SMA tumors revealed major transcriptome overlap with KS tumor biopsies. RacCA tumorigenesis was linked to male gender, and involved ROS activation of angiogenesis and cell proliferation. Furthermore, we found that AIDS-KS lesions and KSHV-infected tumors from our KS mouse model (mouse endothelial cell KSHV Bac36- mECK36) over-express Rac1 in all KSHV-infected (LANA+ve) cells. Moreover, we found that KS lesions and mECK36 lesions over-express key members of the NOX family and that mECK36 tumors upregulate NOX members in a KSHV dependent fashion. This led us to test the ability of N-acetyl cysteine (NAC), a well characterized antioxidant, to suppress mECK36 tumors in mice. We found that NAC prevented KSHV-induced tumor formation. Interestingly, we also found that NAC inibited VEGF, c-myc and viral gene expression in the mECK36 tumors through a mechanism involving platelet derived growth factor (PDGF) receptor and ligand downregulation. These data indicate that Rac1, NOX, ROS, and their downstream effectors are molecules actively involved in KS viral oncogenesis, and suggest that Rac1 signaling and oxidative stress could be attractive KS chemopreventive and therapeutic targets. We proposse to: Study mechanisms and role of Rac1 activation in KSHV oncogenesis (Aim 1), study the role of NADPH oxidase induction of ROS in KSHV oncogenesis (Aim 2) and to test the efficacy of pharmacologic ROS inhibition on prevention and treatment of RacCA and KSHV-induced tumors (Aim 3). PUBLIC HEALTH RELEVANCE: Kaposi's sarcoma (KS) is the most common type of cancer associated with AIDS (AIDS-KS). KS arises as multifocal lesions in the skin, lungs and gastrointestinal tract characterized by intense blood microvessel and cellular proliferation. Early KS lesions are treated with local and non-toxic therapies; however, advanced KS generally characterized as an advanced disseminated cancer with increased morbidity and mortality is treated with systemic chemotherapy. This treatment is difficult to tolerate for AIDS patients who are receiving Anti Retroviral regimes such as HAART. Thus, the development of rational therapies based on KS pathogenesis is critical to fill this gap. The identification of human and viral genes that are the cause of KS carcinogenesis is important because it could lead to the identification of new therapeutic targets. Essential to this work is the creation of animal models of the disease. Two laboratories of UM/SCCC we have succeeded in generating such a models and identifying a host gene named Rac that by itself can cause in mice many aspects of Kaposi's sarcoma. These models and insights are a very good combination to study mechanisms of Kaposi's sarcoma carcinogenesis. We will study how the Rac gene may participate in cell transformation and tumorigenesis. One of the ways this gene may participate in carcinogenesis is by promoting oxidative stress that can lead to cellular damage and genetic damage that could lead to carcinogenic mutations that may contribute to cancer. So we are going to explore ways of preventing this oxidative genetic damage as a means of preventing and possibly curing Kaposi's sarcoma. So our work will allow us to not only to identify mechanisms of KS carcinogenesis but also will help to identify potential new target and new drugs for anti-KS therapy.